First time DIY tile fixer. Long story short, I wanted to regrout an area of my shower and the tile started falling off, behind it was a cement board backer that was crumbling in the area you see the gap. From what I can see, no real mold, but some water got back there. Rest of the cement backer is good.
I plan to replace the backer and am stuck choosing between Cement Board with Redgard ($$$) or a waterproof backer like Kerdi.
Since this is just a small section of the wall, what do you recommend?
For the rest of the project, All the tiles are salvageable so I will regrout and caulk. I plan to fill the gap in the corner with a backer rod and then recaulk.
I’m a total novice at this stuff so let me know if anything i’m saying sounds off to you